Technical Field
The present invention relates to phase shifters and, more particularly, to providing variable loads for reflection-type phase shifters.
Description of the Related Art
Directional transmitters and receivers allow signals to be transmitted and received to/from specific directions while attenuating signals to/from other directions. Electronic steering of the preferred direction of the signal beam can be accomplished by using multiple transmitters and receivers with variable phase shift capability. Electronic variation of the phase shift results in steering the beam direction.
Typical beam steering applications need precise control of the beam pattern, both in the peak angle as well as in filtering. This uses amplitude control as well as variable phase shift in each transmitter/receiver element. To simplify pattern generation, amplitude control is separated from phase control. Such separation needs a relatively constant loss or gain in the variable phase shifter across phase shift values. Conventional phase shifters often use varactors to provide a variation in phase shift values, but varactors often vary in quality and factor and loss with the value of the capacitance. As such, implementing a termination for a reflection-type phase shifter using varactors leads to losses that vary with the phase shift. While an amplifier may be used to compensate for these losses, using active components defeats part of the purpose of using a reflection-type phase shifter.